1. Technical Field
The present invention relates to a pump apparatus and more particularly relates to a pump apparatus provided with a tube pump that rotates while pressing a flexible tube.
2. Related Art
For example, in a liquid ejecting apparatus provided with a liquid ejecting head that ejects a liquid onto a medium (a sheet of paper) to perform a process of recording an image or the like, the liquid ejecting apparatus is equipped with a head maintenance mechanism in order to maintain ejection characteristics with which the liquid is suitably ejected from the liquid ejecting head.
In order to maintain various ejection characteristics, in the head maintenance mechanism, for example, the ejection characteristics are recovered by covering the liquid ejecting head with a suction cap and sucking a liquid having increased viscosity from a nozzle by using the suction pump. At this time, a so-called tube pump is often used as the suction pump. The tube pump turns (rotates) a rotary member around a pump shaft driven by a driving power source (a motor) so that the rotary member rotates while pressing a flexible tube.
In a liquid ejecting apparatus, as described in, for example, JP-A-2005-144690, a motor (a paper transport motor) shares a driving power source with a tube pump (an ink suction unit), and thereby the size of the apparatus is decreased. That is, the motor drives the tube pump in one of opposite rotary directions and transports the paper in the other of the opposite rotary directions.
As is well known, when a pump shaft of the tube pump rotates in a given one direction, a rotary member moves away in the outward direction from a rotary axis of the tube pump and the moved rotary member presses the flexible tube due to the radial movement, while the rotary member is rotated around the pump shaft. When the rotary member rotates in one direction while maintaining the position thereof away from the rotary axis, the rotary member presses the flexible tube. A fluid in the tube is ejected in one direction by the rotation of the rotary member, and thereby an operation of sucking the fluid is performed. Thus, the tube pump serves as a suction pump.
Accordingly, in the case where a liquid having a high degree of viscosity is to be sucked from the nozzle, if a motor rotates in, for example, a normal direction to rotate the rotary member of the tube pump in a given direction to perform a suction operation and then the motor stops rotating temporarily, the tube pump stops the rotary member from rotating in the one direction, thereby ceasing the sucking operation. At this time, there is a case where the rotary member in the tube pump is turned in a direction opposite to the one direction by a reaction force from the pressed flexible tube and the rotary member moves in the inward direction. As a result, the pressing state of the flexible tube, that is, a state in which the sucking operation is able to be performed cannot be maintained and the pressing state is released. Thus, in the case where the rotary member starts rotation again in the normal direction to suck the liquid having increased viscosity, it is necessary for the rotary member to move away in the outward direction from the rotary axis so as to press the flexible tube until the state in which the sucking operation is able to be performed is restored. Thus, there is a problem that the amount of ink that is sucked is unstable due to this rotation.